Forksheet transistor architectures

ABSTRACT

Embodiments disclosed herein include a semiconductor device. In an embodiment, the semiconductor device comprises a first transistor strata. The first transistor strata comprises a first backbone, a first transistor adjacent to a first edge of the first backbone, and a second transistor adjacent to a second edge of the first backbone. In an embodiment, the semiconductor device further comprises a second transistor strata over the first transistor strata. The second transistor strata comprises a second backbone, a third transistor adjacent to a first edge of the second backbone, and a fourth transistor adjacent to a second edge of the second backbone.

TECHNICAL FIELD

Embodiments of the present disclosure relate to semiconductor devices,and more particularly to forksheet transistors with variousarchitectures and interconnects.

BACKGROUND

For the past several decades, the scaling of features in integratedcircuits has been a driving force behind an ever-growing semiconductorindustry. Scaling to smaller and smaller features enables increaseddensities of functional units on the limited real estate ofsemiconductor chips. For example, shrinking transistor size allows forthe incorporation of an increased number of memory or logic devices on achip, lending to the fabrication of products with increased capacity.The drive for ever-more capacity, however, is not without issue. Thenecessity to optimize the performance of each device becomesincreasingly significant.

In the manufacture of integrated circuit devices, multi-gatetransistors, such as tri-gate transistors, have become more prevalent asdevice dimensions continue to scale down. In conventional processes,tri-gate transistors are generally fabricated on either bulk siliconsubstrates or silicon-on-insulator substrates. In some instances, bulksilicon substrates are preferred due to their lower cost and becausethey enable a less complicated tri-gate fabrication process. In anotheraspect, maintaining mobility improvement and short channel control asmicroelectronic device dimensions scale below the 10 nanometer (nm) nodeprovides a challenge in device fabrication. Nanowires used to fabricatedevices provide improved short channel control.

Scaling multi-gate and nanowire transistors has not been withoutconsequence, however. As the dimensions of these fundamental buildingblocks of microelectronic circuitry are reduced and as the sheer numberof fundamental building blocks fabricated in a given region isincreased, the constraints on the lithographic processes used to patternthese building blocks have become overwhelming. In particular, there maybe a trade-off between the smallest dimension of a feature patterned ina semiconductor stack (the critical dimension) and the spacing betweensuch features.

In order to combat the demands of spacing between features, a forksheettransistor architecture has been proposed. In a forksheet architecture,an insulating backbone is disposed between a first transistor and asecond transistor. The semiconductor channels (e.g., ribbons, wires,etc.) of the first transistor and the second transistor contact oppositesidewalls of the backbone. As such, the spacing between the firsttransistor and the second transistor is reduced to the width of thebackbone. Since one surface of the semiconductor channels contacts thebackbone, such architectures do not allow for gate all around (GAA)control of the semiconductor channels. Additionally, compactinterconnect architectures between the first transistor and the secondtransistor have yet to be proposed.

BRIEF DESCRIPTION OF TH_(B) DRAWINGS

FIG. 1A is a perspective view illustration of forksheet transistors.

FIG. 1B is a cross-sectional illustration of forksheet transistorsacross the semiconductor channels.

FIGS. 2A-2C are cross-sectional illustrations of stacked forksheettransistors, in accordance with various embodiments.

FIGS. 3A-3D are cross-sectional illustrations depicting a process forfabricating self-aligned stacked forksheet transistors, in accordancewith an embodiment.

FIGS. 4A and 4B are cross-sectional illustrations of stacked forksheettransistors with an interconnect between gate electrodes of a pair ofthe forksheet transistors, in accordance with various embodiments.

FIGS. 5A-5B are cross-sectional illustrations of stacked forksheettransistors with an interconnect between source/drain regions of a pairof the forksheet transistors, in accordance with various embodiments.

FIG. 6 is a cross-sectional illustration of stacked forksheettransistors with an interconnect to a source/drain region from a bottomcontact, in accordance with an embodiment.

FIG. 7 is a cross-sectional illustration of stacked forksheettransistors with an interconnect to a gate electrode from a bottomcontact, in accordance with an embodiment.

FIG. 8A is a perspective view illustration of forksheet transistors withbackbones that comprise a liner, in accordance with an embodiment.

FIGS. 8B-8D are cross-sectional illustrations of the forksheettransistors in FIG. 8A along different planes, in accordance with anembodiment.

FIGS. 9A and 9B are cross-sectional illustrations of the forksheettransistors in FIG. 8A, in accordance with an additional embodiment.

FIGS. 10A-10L are cross-sectional illustrations depicting a process forfabricating forksheet transistors with liners along the backbones, inaccordance with an embodiment.

FIG. 11A is a cross-sectional illustration of forksheet transistors witha catalytic oxidant material for the liner over the backbones, inaccordance with an embodiment.

FIGS. 11B and 11C are zoomed in illustrations that illustrate thetopography of the liner proximate to the semiconductor channel, inaccordance with various embodiments.

FIGS. 12A-12D are cross-sectional illustrations depicting a process forfabricating forksheet transistors with a liner comprising a catalyticoxidant material, in accordance with an embodiment.

FIGS. 13A-13C are cross-sectional illustrations depicting a process forfabricating forksheet transistors with electrically coupled gateelectrodes across the backbone with a timed etching process, inaccordance with an embodiment.

FIG. 13D is a plan view illustration of the forksheet transistors inFIG. 13C, in accordance with an embodiment.

FIGS. 14A-14C are cross-sectional illustrations depicting a process forfabricating forksheet transistors with electrically coupled gateelectrodes across the backbone with an etchstop layer in the backbone,in accordance with an embodiment.

FIGS. 15A-15D are cross-sectional illustrations of forksheet transistorswith etchstop layers in various locations within the backbone, inaccordance with various embodiments.

FIGS. 16A-16D are cross-sectional illustrations of a backbone with anembedded etchstop layer, in accordance with various embodiments.

FIG. 17A is a cross-sectional illustration of forksheet transistors withan interconnect between source/drain regions across the backbone, inaccordance with an embodiment.

FIG. 17B is a plan view illustrations of the forksheet transistors inFIG. 17A, in accordance with an embodiment.

FIG. 18 is a plan view illustration of forksheet transistors that areconfigured as an inverter by interconnects across the backbone, inaccordance with an embodiment.

FIGS. 19A-19C are cross-sectional illustrations of forksheet transistorsthat comprise an etch selective layer between the source/drain regionsand a bottom contact, in accordance with various embodiments.

FIGS. 20A and 20B are cross-sectional illustrations of forksheettransistors that comprise different etch selective layers between thesource/drain regions an bottom contacts, in accordance with variousembodiments.

FIG. 21 illustrates a computing device in accordance with oneimplementation of an embodiment of the disclosure.

FIG. 22 is an interposer implementing one or more embodiments of thedisclosure.

EMBODIMENTS OF THE PRESENT DISCLOSURE

Described herein are forksheet transistors with various architecturesand interconnect schemes, in accordance with various embodiments. In thefollowing description, various aspects of the illustrativeimplementations will be described using terms commonly employed by thoseskilled in the art to convey the substance of their work to othersskilled in the art. However, it will be apparent to those skilled in theart that the present invention may be practiced with only some of thedescribed aspects. For purposes of explanation, specific numbers,materials and configurations are set forth in order to provide athorough understanding of the illustrative implementations. However, itwill be apparent to one skilled in the art that the present inventionmay be practiced without the specific details. In other instances,well-known features are omitted or simplified in order not to obscurethe illustrative implementations.

Various operations will be described as multiple discrete operations, inturn, in a manner that is most helpful in understanding the presentinvention, however, the order of description should not be construed toimply that these operations are necessarily order dependent. Inparticular, these operations need not be performed in the order ofpresentation.

As noted above, forksheet transistors allow for increased density ofnon-planar transistor devices. An example of semiconductor device 100with forksheet transistors 120 _(A) and 120 _(B) is shown in FIG. 1A. Aforksheet transistor includes a backbone 110 that extends up from asubstrate 101 with a transistor 120 adjacent to the either sidewall ofthe backbone 110. As such, the spacing between transistors 120 _(A) and120 _(B) is equal to the width of the backbone 110. Therefore, thedensity of such forksheet transistors 120 can be increased compared toother non-planar transistor architectures (e.g., fin-FETs, nanowiretransistors, etc.).

Sheets 105 of semiconductor material extend away (laterally) from thebackbone 110. In the illustration of FIG. 1A, sheets 105 _(A) and 105_(B) are shown on either side of the backbone 110. The sheets 105 _(A)are for the first transistor 120 _(A) and the sheets 105 _(B) are forthe second transistor 120 _(B). The sheets 105 _(A) and 105 _(B) passthrough a gate structure 112. The portions of the sheets 105 _(A) and105 _(B) within the gate structure 112 are considered the channel, andthe portions of the sheets 105 _(A) and 105 _(B) on opposite sides ofthe gate structure 112 are considered source/drain regions. In someimplementations, the source/drain regions comprise an epitaxially grownsemiconductor body, and the sheets 105 may only be present within thegate structure 112. That is, the stacked sheets 105 _(A) and 105 _(B)are replaced with a block of semiconductor material.

Referring now to FIG. 1B, a cross-sectional illustration of thesemiconductor device 100 through the gate structure 112 is shown. Asshown, vertical stacks of semiconductor channels 106 _(A) and 106 _(B)are provided through the gate structure 112. The semiconductor channels106 _(A) and 106 _(B) are connected out of the plane of FIG. 1B to thesource/drain regions. The semiconductor channels 106 _(A) and 106 _(B)are surrounded on three sides by a gate dielectric 108. The surfaces 107of the semiconductor channels 106 _(A) and 106 _(B) are in directcontact with the backbone 110. A workfunction metal 109 may surround thegate dielectric 108, and a gate fill metal 113 _(A) and 113 _(B) maysurround the workfunction metal 109. In the illustration, thesemiconductor channels 106 _(A) and 106 _(B) are shown as havingdifferent shading. However, in some implementations, the semiconductorchannels 106 _(A) and 106 _(B) may be the same material. An insulatorlayer 103 may be disposed over the gate fill metals 113 _(A) and 113_(B).

While such forksheet transistors 120 _(A) and 120 _(B) provide manybenefits, there are still many areas for improvement in order to providehigher densities, improved interconnection architectures, and improvedperformance. For example, embodiments disclosed herein provide furtherdensity improvements by stacking a plurality of transistor strata overeach other. Whereas the semiconductor device 100 in FIGS. 1A and 1Billustrate a single strata (i.e., a pair of adjacent forksheettransistors 120 _(A) and 120 _(B)), embodiments disclosed hereincomprise a first strata and a second strata (e.g., to provide fourforksheet transistors) within the same footprint illustrated in FIGS. 1Aand 1B. Additionally, embodiments disclosed herein provide interconnectarchitectures that allow for electrical coupling between the firststrata and the second strata to effectively utilize the multiple strata.Additionally, embodiments disclosed herein include interconnectarchitectures that allow for bottom side connections to the buriedstrata.

Embodiments disclosed herein also include forksheet transistors witharchitectures that allow for gate-all-around (GAA) control of thesemiconductor channels. Whereas existing forksheet transistors include asurface of the semiconductor channels that is in direct contact with thebackbone, embodiments disclosed herein comprise various linerarchitectures for the backbone that allow for semiconductor channels tobe spaced away from the backbone. In some embodiments, the liner iscompletely removed in the gate region. In other embodiments, the linercomprises a catalytic oxidant that allows for selective removal ofportions of the liner adjacent to the semiconductor channels or forremoval of a portion of the semiconductor immediately adjacent to thecatalytic oxidant material.

Embodiments disclosed herein also comprise interconnect architecturesthat allow for interconnections between forksheet transistors within thesame strata. For example, embodiments include interconnects that passacross the backbone in order to connect source/drain regions and/or gateelectrodes of neighboring forksheet transistors. In some embodiments,the interconnects are formed with a timed etching process. In otherembodiments, the interconnects are formed using an etchstop layer thatis embedded in the backbone.

Embodiments disclosed herein also comprise architectures for providingselective interconnects to contacts that underlie the forksheettransistors (i.e., bottom side contacts). The selective bottom sidecontact formation is implemented using an etch selective layer below theforksheet transistors. The etch selective layer may be aligned withoverlying semiconductor channels in some embodiments. In somearchitectures disclosed herein, etch selective layers that comprise thesame material are below both neighboring forksheet transistors. In otherembodiments, a first etch selective layer is below a first forksheettransistor, and a second etch selective layer (that has a different etchselectivity than the first etch selective layer) is below theneighboring second forksheet transistor.

Referring now to FIG. 2A, a cross-sectional illustration of asemiconductor device 200 is shown, in accordance with an embodiment. Thecross-sectional illustration in FIG. 2A is through the gate region andperpendicular to the semiconductor channels 206. The semiconductordevice 200 comprises a first strata of forksheet transistors 220 _(A)and 220 _(B) and a second strata of forksheet transistors 220 _(C) and220 _(D) over the first strata. In an embodiment, an insulating layer214 may separate the first strata from the second strata. The insulatinglayer 214 may be part of an insulating layer 203 that surrounds bothstrata. In other embodiments, the insulating layer 214 may be a discretelayer from the insulating layer 203.

In an embodiment, the first strata and the second strata may be disposedover a substrate 201. In an embodiment, the substrate 201 is aninsulating layer. The substrate 201 may overly a semiconductor substratein some embodiments. In an embodiment, the underlying semiconductorsubstrate represents a general workpiece object used to manufactureintegrated circuits. The semiconductor substrate often includes a waferor other piece of silicon or another semiconductor material. Suitablesemiconductor substrates include, but are not limited to, single crystalsilicon, polycrystalline silicon and silicon on insulator (SOI), as wellas similar substrates formed of other semiconductor materials, such assubstrates including germanium, carbon, or group III-V materials.

In the illustrated embodiment, the first strata comprises forksheettransistors 220 _(A) and 220 _(B) that have a first conductivity type,and the second strata comprises forksheet transistors 220 _(C) and 220_(D) that have a second conductivity type. For example, the first stratamay comprise P-type transistors 220 and the second strata may compriseN-type transistors 220. However, in other embodiments one or both of thefirst strata and the second strata may comprise transistors 220 withboth conductivity types. For example, the first transistor 220 _(A) maybe P-type and the second transistor 220 _(B) may be N-type. In theillustrated embodiment, each of the transistors 220 are shown as havingthree semiconductor channels 206. However, it is to be appreciated thatany number of semiconductor channels 206 may be used in the varioustransistors 220.

In an embodiment, the first strata may comprise a first backbone 210_(A). Semiconductor channels 206 may extend out (laterally) from thefirst backbone 210 _(A). In an embodiment, the semiconductor channels206 may comprise material such as, but not limited to, silicon,germanium, SiGe, GaAs, InSb, GaP, GaSb, InAlAs, InGaAs, GaSbP, GaAsSb,and InP. In some embodiments, a surface of the semiconductor channels206 may directly contact an edge of the first backbone 210 _(A). Inother embodiments (as will be described in greater detail below) thesemiconductor channels 206 may be spaced away from the first backbone210 _(A). In the illustrated embodiment, the semiconductor channels 206are shown as having a substantially rectangular cross-section. However,it is to be appreciated that the cross-section of the semiconductorchannels 206 may have any suitable shape. In some instances, thesemiconductor channels 206 may be referred to as nanoribbons ornanowires.

In an embodiment, a perimeter of the semiconductor channels 206 may be(at least partially) surrounded by a gate dielectric 208. The gatedielectric 208 may be, for example, any suitable oxide such as silicondioxide or high-k gate dielectric materials. Examples of high-k gatedielectric materials include, for instance, hafnium oxide, hafniumsilicon oxide, lanthanum oxide, lanthanum aluminum oxide, zirconiumoxide, zirconium silicon oxide, tantalum oxide, titanium oxide, bariumstrontium titanium oxide, barium titanium oxide, strontium titaniumoxide, yttrium oxide, aluminum oxide, lead scandium tantalum oxide, andlead zinc niobate. In some embodiments, an annealing process may becarried out on the gate dielectric 208 layer to improve its quality whena high-k material is used.

In an embodiment, a workfunction metal 209 may surround the gatedielectric 208. When the workfunction metal 209 will serve as an N-typeworkfunction metal, the workfunction metal 209 preferably has aworkfunction that is between about 3.9 eV and about 4.2 eV. N-typematerials that may be used to form the workfunction metal 209 include,but are not limited to, hafnium, zirconium, titanium, tantalum,aluminum, and metal carbides that include these elements, i.e., titaniumcarbide, zirconium carbide, tantalum carbide, hafnium carbide andaluminum carbide. When the workfunction metal 209 will serve as a P-typeworkfunction metal, the workfunction metal preferable has a workfunctionthat is between about 4.9 eV and about 5.2 eV. P-type materials that maybe used to form the workfunction metal 209 include, but are not limitedto, ruthenium, palladium, platinum, cobalt, nickel, and conductive metaloxides, e.g., ruthenium oxide.

In an embodiment, a gate fill metal 213 may surround the workfunctionmetal 209. The gate fill metal 213 may comprise a wide range ofmaterials, such as polysilicon, silicon nitride, silicon carbide, orvarious suitable metals or metal alloys, such as aluminum, tungsten,titanium, tantalum, copper, titanium nitride, or tantalum nitride, forexample. The combination of the gate fill metal 213 and the workfunctionmetal 209 may sometimes be referred to herein as a gate electrode forsimplicity.

In an embodiment, the second strata may comprise a second backbone 210_(B). The third transistor 220 _(C) and the fourth transistor 220 _(D)may be positioned on opposing edges of the second backbone 210 _(B). Thestructures and materials for the third transistor 220 _(C) and thefourth transistor 220 _(D) may be substantially similar to thosedescribed above with respect to the first transistor 220 _(A) and thesecond transistor 220 _(B).

In an embodiment, the first strata and the second strata may befabricated with different processing flows. That is, the first stratamay be fabricated using a first lithography process, and the secondstrata may be fabricated using a second lithography process. As such,there may be some registration error between the first strata and thesecond strata due to overlay limits of existing lithography tools. Forexample, a registration error M is shown in FIG. 2A. That is, an edge ofthe first backbone 210 _(A) may be misaligned with respect to an edge ofthe second backbone 210 _(B).

In order to eliminate the registration error M, some embodimentsdisclosed herein utilize a self-aligned process to form stacked strataof forksheet transistors. An example of such an embodiment is shown inFIG. 2B.

As shown in FIG. 2B, the semiconductor device 200 includes a firststrata (i.e., first transistor 220 _(A) and second transistor 220 _(B))and a second strata (i.e., third transistor 220 _(C) and fourthtransistor 220 _(D)). The semiconductor device 200 in FIG. 2B issubstantially similar to the semiconductor device 200 in FIG. 2A, withthe exception that a single backbone 210 is provided, and there is noregistration error between the two strata. In an embodiment, the firststrata and the second strata of transistors 220 may both be adjacent tothe backbone 210. The elimination of the registration error between thestrata is made possible by using a self-aligned fabrication process. Forexample, a single lithography operation is used to pattern the backbone210 (used by both strata), and a single lithography operation is used topattern the semiconductor channels 206 of both strata. A more detailedexplanation of such a self-aligned process flow is provided with respectto FIGS. 3A-3D below.

Referring now to FIG. 2C, a cross-sectional illustration of asemiconductor device 200 is shown, in accordance with an additionalembodiment. The semiconductor device 200 in FIG. 2C is substantiallysimilar to the semiconductor device 200 in FIG. 2B, with the exceptionthat a third strata (i.e., fifth transistor 220 _(E) and sixthtransistor 220 _(F)) are positioned above the second strata. As shown,the third strata is also self-aligned with the underlying strata, andshares the single backbone 210. While examples of two strata and threestrata are shown herein, it is to be appreciated that a semiconductordevice 200 may be implemented with any number of stacked strata. Theplurality of stacked strata may be implemented with a self-alignedprocess (e.g., similar to FIGS. 2B and 2C) or with discrete processing(e.g., similar to FIG. 2A).

Referring now to FIGS. 3A-3D a series of illustrations depicting aprocess for fabricating self-aligned stacked forksheet transistors isshown, in accordance with an embodiment.

Referring now to FIG. 3A, a perspective view illustration of asemiconductor device 300 is shown, in accordance with an embodiment. Inan embodiment, the semiconductor device 300 comprises a substrate 301and a plurality of epitaxially grown layers 393, 394 over the substrate301. The layers 393, 394 may be arranged into a first strata 391 and asecond strata 392 over the first strata 391. The layers 393 may be asemiconductor material that is to be used for the channels of transistordevices. For example, the layers 393 may comprise silicon. The layers394 may be sacrificial layers that are etch selective to the layers 393.For example, when layer 393 is silicon, layer 394 may comprise silicongermanium. In an embodiment, the layers 393 and 394 may be patternedinto a fin. In another embodiment, the layers 393 may be comprised ofsemiconductor layers and the layers 394 may be comprised of dielectriclayers such as silicon dioxide, silicon nitride, silicon oxynitride.

Referring now to FIG. 3B, a perspective view illustration of thesemiconductor device 300 after a backbone trench 395 is formed throughthe first strata 391 and the second strata 392. A single lithographicoperation provides a self-alignment between the portion of the backbonebetween the first strata 391 and the portion of the backbone between thesecond strata 392. In an embodiment, the backbone trench 395 may beformed with one or more etching processes. The backbone trench 395defines the plurality of transistor devices 320 in the semiconductordevice 300. A first transistor 320 _(A) and a second transistor 320 _(B)are in the first strata 391, and a third transistor 320 _(C) and afourth transistor 320 _(D) are in the second strata 392.

Referring now to FIG. 3C, a perspective view illustration of thesemiconductor device 300 after a backbone 310 is disposed in thebackbone trench 395. The backbone 310 is an insulative material. Thebackbone 310 may be deposited with any suitable deposition process. Insome embodiments, portions of the backbone 310 outside of the backbonetrench 395 may be remove with an etching process.

Referring now to FIG. 3D, a perspective view illustration of thesemiconductor device 300 after the formation of source/drain regions 305and the gate electrode 313 is shown, in accordance with an embodiment.The formation of the source/drain regions 305 may be implemented usingstandard processes. In an embodiment, a portion 314 of insulating layer303 may separate the source/drain regions 305 in the first transistor320 _(A) from the source/drain regions 305 in the third transistor 320_(C), and the portion 314 may separate the source/drain regions 305 inthe second transistor 320 _(B) from the source/drain regions 305 in thefourth transistor 320 _(D). Some details of the semiconductor device 300(e.g., spacers) are omitted from FIG. 3D for simplicity.

Referring now to FIG. 4A, a cross-sectional illustration ofsemiconductor device 400 with stacked forksheet transistors is shown, inaccordance with an embodiment. The semiconductor device 400 may comprisea backbone 410 disposed over a substrate 401. A first strata comprisinga first transistor 420 _(A) and a second transistor 420 _(B) may bepositioned below a second strata comprising a third transistor 420 _(C)and a fourth transistor 420 _(D). Each transistor 420 may includesemiconductor channels 406. An insulating layer 403 may surround thefirst and second strata.

In an embodiment, the semiconductor device 400 may be substantiallysimilar to the semiconductor device 200 in FIG. 2B, with the exceptionthat an interconnect 415 is disposed through the insulating layer 414between the first strata and the second strata to connect the gateelectrode 413 of the second transistor 420 _(B) to the gate electrode413 of the fourth transistor 420 _(D). In an embodiment, theinterconnect 415 may be the same material as the gate electrode 413.However, in other embodiments, such as the embodiment illustrated inFIG. 4B, the interconnect 415 may be a different material than thematerial of the gate electrodes 413.

In an embodiment, gate electrode 413 of the first transistor 420 _(A)may be electrically isolated from the gate electrode 413 of the thirdtransistor 420 _(C) by the insulating layer 414. Additionally, whenlooking globally at various locations on a semiconductor die, someforksheet transistor stacks may include interconnects 415 to connectstacked gate electrodes 413, and other forksheet transistor stacks mayinclude no interconnect 415 between stacked gate electrodes 413. In yetanother embodiment, a first interconnect 415 may be included between thegate electrode 413 of the first transistor 420 _(A) and the gateelectrode 413 of the third transistor 420 _(C), and a secondinterconnect 415 may be included between the gate electrode 413 of thesecond transistor 420 _(B) and the gate electrode 413 of the fourthtransistor 420 _(D). In the illustrated embodiment, a self-alignedarchitecture between the first strata and the second strata is shown.However, it is to be appreciated that substantially similarinterconnects 415 between gate electrodes 413 may be implemented usingan architecture similar to that of FIG. 2A.

Referring now to FIG. 5A, a cross-sectional illustration of asemiconductor device 500 is shown, in accordance with an embodiment. Theplane shown is perpendicular to the channel and through the source/drainregions 505. That is, a source/drain region 505 for each of thetransistors 520 _(A-D) on either side of the backbone 510 is shown. Alsoillustrated is a substrate 501 and an insulating layer 503 around thetransistors 520.

In an embodiment, the source/drain regions 505 are arbitrarily shaped.This is due to the source/drain regions 505 being epitaxially grown fromthe semiconductor channels (not shown). In some embodiments, thesource/drain regions 505 may contact the backbone 510. In otherembodiments, the source/drain regions 505 are spaced away from thebackbone 510, as shown in FIG. 5A. The source/drain regions 505 may beformed by conventional processes. For example, recesses adjacent to thegate stack are formed with an etching process. The recessing may exposeends of the semiconductor channels within the gate stack. These recessesmay then be filled with a semiconductor using a selective epitaxialdeposition process that grows from the ends of the semiconductorchannels. In some implementations, the epitaxial semiconductor may bein-situ doped. For example, the epitaxial semiconductor may comprisein-situ doped silicon germanium, in-situ doped silicon carbide, orin-situ doped silicon. In alternate implementations, other siliconalloys may be used. For instance, alternate silicon alloy materials thatmay be used include, but are not limited to, nickel silicide, titaniumsilicide, cobalt silicide, and possibly may be doped with one or more ofboron and/or aluminum.

In an embodiment, an interconnect 516 may be provided to electricallycouple source/drain regions 505 in different strata of the semiconductordevice 500. For example, an interconnect 516 provides an electricalconnection between the source/drain region 505 of the fourth transistor520 _(D) and the second transistor 520 _(B). The interconnect 516 maypass through an insulating layer 514 between the strata. In anembodiment, the interconnect 516 may be formed with any suitableprocess. For example, a trench may be etched into the source/drainregions 505 and filled with a conductive material. In the illustratedembodiment, the interconnect 516 passes completely through thesource/drain region 505 of the fourth transistor 520 _(D) and into (butnot through) the source/drain region 505 of the second transistor 520_(B).

In an embodiment, source/drain region 505 of the first transistor 520_(A) may be electrically isolated from the source/drain region 505 ofthe third transistor 520 _(C) by the insulating layer 514. Additionally,when looking globally at various locations on a semiconductor die, someforksheet transistor stacks may include interconnects 516 to connectstacked source/drain regions 505, and other forksheet transistor stacksmay include no interconnect 516 between stacked source/drain regions505. In yet another embodiment, a first interconnect 516 may be includedbetween the source/drain region 505 of the first transistor 520 _(A) andthe source/drain region 505 of the third transistor 520 _(C), and asecond interconnect 516 may be included between the source/drain region505 of the second transistor 520 _(B) and the source/drain region 505 ofthe fourth transistor 520 _(D). In the illustrated embodiment, aself-aligned architecture between the first strata and the second stratais shown. However, it is to be appreciated that substantially similarinterconnects between source/drain regions 505 may be implemented usingan architecture similar to that of FIG. 2A.

Referring now to FIG. 5B, a cross-sectional illustration of thesemiconductor device 500 in FIG. 5_(A) along line B-B′ is shown, inaccordance with an embodiment. The plane of FIG. 5B is parallel to thesemiconductor channels 506. As shown, a pair of source/drain regions 505are on opposite ends of the semiconductor channels 506 for eachtransistor 520. In an embodiment, spacers 511 may define a channelregion. The channel region may comprise a gate dielectric 508surrounding the semiconductor channels 506 and a gate electrode 513surrounding the gate dielectric 508. The workfunction metal between thegate electrode 513 and the gate dielectric 508 is omitted forsimplicity.

As shown, the interconnect 516 extends through the source/drain region505 of the fourth transistor 520 _(D) and into the source/drain region505 of the second transistor 520 _(B). The interconnect 516 may bealigned with an edge of the source/drain regions 505. In otherembodiments, the interconnect 516 may be entirely within a width of thesource/drain regions 505.

Referring now to FIG. 5C, a cross-sectional illustration of asemiconductor device 500 is shown, in accordance with an additionalembodiment. The semiconductor device 500 in FIG. 5C is substantiallysimilar to the semiconductor device 500 in FIG. 5B, with the exceptionthat the interconnect 516 does not pass into the source/drain region 505of the second transistor 520 _(B). Instead, the interconnect 516 landson a top surface of the source/drain region 505 of the second transistor520 _(B).

Referring now to FIG. 5D, a cross-sectional illustration of asemiconductor device 500 is shown, in accordance with anotherembodiment. The semiconductor device 500 in FIG. 5D is substantiallysimilar to the semiconductor device 500 in FIG. 5B, with the exceptionthat the interconnect 516 passes entirely through the source/drainregion 505 of the second transistor 520 _(B).

Referring now to FIG. 5E, a cross-sectional illustration of asemiconductor device 500 is shown, in accordance with yet anotherembodiment. The semiconductor device 500 in FIG. 5B is substantiallysimilar to the semiconductor device 500 in FIG. 5B, with the exceptionthat the interconnect 516 does not pass into either of the source/drainregions 505. Instead, the interconnect 516 wraps around one or moreouter surfaces of one or both of the source/drain regions 505 of thefourth transistor 520 _(D) and the second transistor 520 _(B).

In FIGS. 4A-5E, examples of either gate electrode 413 interconnects 415between strata (e.g., FIGS. 4A and 4B) or source/drain region 505interconnects 516 between strata (e.g., FIGS. 5A-5E) are shown. However,it is to be appreciated that in some embodiments, a semiconductor devicewith stacked forksheet transistors may include both a source/drainregion interconnect 516 and a gate electrode interconnect 415 betweenthe strata.

In addition to providing interconnections between stacked strata ofsemiconductor device, embodiments also include providing interconnectsto contacts below the forksheet transistors. In this way, the buriedforksheet transistors (i.e., the first strata of transistors) can becontacted without having to pass through the overlying transistors.Examples of such configurations are provided in FIGS. 6 and 7.

Referring now to FIG. 6, a cross-sectional illustration of asemiconductor device 600 is shown, in accordance with an embodiment. Inan embodiment, the semiconductor device 600 may comprise a substrate 601and forksheet transistors 620 _(A-D) over the substrate 601. A backbone610 may separate the first transistor 620 _(A) from the secondtransistor 620 _(B) and separate the third transistor 620 _(C) from thefourth transistor 620 _(D). The plane of the cross-section is throughthe source/drain regions 605 of the transistors 620. In an embodiment,an insulating layer 603 may surround the transistors 620.

In an embodiment, conductive features may be provided in the substrate601. For example, a buried line 618 may be positioned adjacent to thestacked transistors 620. Conductive pads 619 may be located below thestacked transistors 620 and connected to the buried line 618 (out of theplane of FIG. 6). In an embodiment, an interconnect 617 may extend fromthe pad 619 to a source/drain region 605 of the first transistor 620_(A). In other embodiments, both the first transistor 620 _(A) and thesecond transistor 620 _(B) may be connected to underlying pads 619 byinterconnects 617. It is to be appreciated that the architecture of theconductive features in FIG. 6 is exemplary in nature, and that anybackside interconnect architecture may be used to contact thesource/drain regions 605 of the transistors 620 _(A) and 620 _(B). Forexample, the backside interconnect architecture may include any numberof layers of routing, vias, pads, and the like.

Referring now to FIG. 7, a cross-sectional illustration of asemiconductor device 700 is shown, in accordance with an embodiment. Theillustrated plane in FIG. 7 is through the channel region. As shown, thesemiconductor device 700 includes a substrate 701 and a plurality ofstacked forksheet transistors 720 _(A-D). Each of the transistors 720comprise semiconductor channels 706 that extend away from the backbone710. A gate stack including a gate electrode 713 and a gate dielectric708 surround portions of the semiconductor channels 706. An insulatinglayer 703 surrounds the transistors 720.

In an embodiment, conductive features may be provided in the substrate701. For example, a buried line 718 may be positioned adjacent to thestacked transistors 720. Conductive pads 719 may be located below thestacked transistors 720 and connected to the buried line 718 (out of theplane of FIG. 7). In an embodiment, an interconnect 717 may extend fromthe pad 719 to a gate electrode 713 of the first transistor 720 _(A). Inother embodiments, both the first transistor 720 _(A) and the secondtransistor 720 _(B) may be connected to underlying pads 719 byinterconnects 717. It is to be appreciated that the architecture of theconductive features in FIG. 7 is exemplary in nature, and that anybackside interconnect architecture may be used to contact the gateelectrodes 713 of the transistors 720 _(A) and 720 _(B). For example,the backside interconnect architecture may include any number of layersof routing, vias, pads, and the like.

As noted above, existing forksheet transistors are not true GAA devices.This is because the semiconductor channels are in direct contact withthe surface of the backbone. Therefore, the surface contacting thebackbone cannot be gated. Accordingly, embodiments disclosed hereininclude forksheet transistor architectures that allow for true GAAcontrol of the semiconductor channels.

Referring now to FIG. 8A, a perspective view illustration of asemiconductor device 800 is shown, in accordance with an embodiment. Thesemiconductor device 800 illustrated in FIG. 8A comprises a firsttransistor 820 _(A), a second transistor 820 _(B), and a thirdtransistor 820 c. The first transistor 820 _(A) is separated from thesecond transistor 820 _(B) by a backbone 810, and the second transistor820 _(B) is separated from the third transistor 820 _(C) by a backbone810. In an embodiment, the first transistor 820 _(A) and the thirdtransistor 820 _(C) are a first conductivity type (e.g., P-type), andthe second transistor 820 _(B) is a second conductivity type (e.g.,N-type). In an embodiment, the transistors 820 are disposed over asubstrate 801.

As shown in FIG. 8A, each transistor 820 comprises a pair ofsource/drain regions 805 that are separated from each other by a gateelectrode 813. The gate electrode 813 may be separated from thesource/drain regions 805 by a spacer 811, as is known to those skilledin the art. Portions of the gate dielectric 808 are also visible betweenthe spacer 811 and the gate electrode 813.

A liner 821 is provide around portions of the backbones 810 in order toprovide the GAA architecture. The liner 821 is visible adjacent to thesource/drain regions 805. However, portions of the liner 821 are removedfrom the channel region (i.e., along the gate electrode 813). The liner821 has a thickness T. In some embodiments, the thickness T may beapproximately 3 nm or greater, or between approximately 3 nm and 6 nm.

Referring now to FIG. 8B, a cross-sectional illustration of thesemiconductor device 800 of FIG. 8A along line B-B′ is shown, inaccordance with an embodiment. As shown, each of the semiconductorchannels 806 has a perimeter that is completely surrounded by the gatedielectric 808 and the gate electrode 813. A workfunction metal (notshown) is also over the gate dielectric 808. The ability to provide sucha GAA architecture is provided by the removal of the liner 821 from thechannel region. Removing the liner 821 leaves a spacing T between anedge of the semiconductor channel 806 and the backbone 810 that is equalto the thickness T of the liner 821. The space T is sufficient to allowfor the deposition of the gate dielectric 808 and the workfunction metalbetween the edge of the semiconductor channel 806 and the edge of thebackbone 810. In some embodiments, portions of the gate dielectric 808may also be deposited along sidewalls of the backbone 810 during aconformal deposition process.

In an embodiment, the entirety of the liner 821 is not removed from thechannel region. For example, a remnant of the liner 821 may be presentalong a bottom surface of the backbone 810. That is, the backbone 810may be separated from the substrate 801 by the liner 821.

Referring now to FIG. 8C, a cross-sectional illustration of thesemiconductor device 800 in FIG. 8A along line C-C′ is shown, inaccordance with an embodiment. As shown, the semiconductor channels 806pass through the spacers 811 to contact the source/drain regions 805.The gate dielectric 808 may cover the surfaces of the channel regionwithin the spacers 811. A portion of the gate dielectric 808 may also bedisposed over the interior surfaces of the spacers 811.

Referring now to FIG. 8D, a cross-sectional illustration of thesemiconductor device 800 in FIG. 8A along line D-D′ is shown, inaccordance with an embodiment. This cross-sectional plane clearlyillustrates portions of the liner 821. As shown, the portions of theliner 821 may wrap around the bottom and sidewalls of the backbone 810adjacent to the source/drain regions 805. That is, the liner 821 mayhave a substantially U-shaped cross-section in some embodiments. Inother embodiments, the liner 821 may be removed from only the regionadjacent to substrate material 801 through a dry etch or similar processresulting in a backbone material 810 which is no longer separated fromthe substrate 801.

Referring now to FIGS. 9A and 9B, cross-sectional illustrations of asemiconductor device 900 are shown, in accordance with an additionalembodiment. The semiconductor device 900 may comprise a substrate 901and a plurality of forksheet transistors 920 _(A-C) over the substrate901. The transistors 920 may comprise semiconductor channels 906completely surrounded by a gate dielectric 908 and a gate electrode 913(FIG. 9A). The transistors 920 may also comprise source/drain regions905 (FIG. 9B).

The semiconductor device 900 in FIGS. 9A and 9B may be substantiallysimilar to the semiconductor device 800 in FIGS. 8A-8D. Particularly,the cross-section in FIG. 9A is similar to the cross-section in FIG. 8B,and the cross-section in FIG. 9B is similar to the cross-section in FIG.8D. The difference between semiconductor device 900 and semiconductordevice 800 is that the liner 921 is removed from the bottom surfaces ofthe backbone 910. As shown in FIG. 9A, there is no remnant of the liner921 in the channel region. Similarly, the bottom portion of the liner921 between the backbone 910 and the substrate 901 is removed in FIG.9_(B) . As such, the liner 921 is no longer substantially U-shaped, andinstead includes a pair of discrete layers on either sidewall of thebackbone 910.

Referring now to FIGS. 10A-10L, a series of illustrations depict aprocess for forming semiconductor devices with forksheet transistorsthat comprise GAA architectures using a liner is shown, in accordancewith an embodiment.

Referring now to FIG. 10A, a perspective view illustration of asemiconductor device 1000 is shown, in accordance with an embodiment. Inan embodiment, the semiconductor device 1000 comprises a substrate 1001and a plurality of layers 1093, 1094 over the substrate 1001. In anembodiment, the layers 1093, 1094 are patterned into a fin. The layers1093 may be a semiconductor material that will be used for the channelsof the semiconductor device 1000, and the layers 1094 may be sacrificiallayers. For example, layers 1093 may be silicon, and layers 1094 may besilicon germanium.

Referring now to FIG. 10B, a perspective view illustration of thesemiconductor device 1000 after a backbone trench 1095 is patterned intothe layers 1093, 1094. The backbone trench 1095 may define a firsttransistor 1020 _(A) and a second transistor 1020 _(B). The backbonetrench 1095 may be patterned with any suitable etching process orprocesses.

Referring now to FIG. 10C, a perspective view illustration of thesemiconductor device 1000 after a backbone liner 1021 is disposed overexposed surfaces is shown, in accordance with an embodiment. In anembodiment, the backbone liner 1021 may be disposed with a conformaldeposition process, so that the backbone liner 1021 lines sidewallsurfaces of the first transistor 1020 _(A) and the second transistor1020 _(B). In some embodiments, the planar surfaces of the backboneliner 1021 (e.g., over the substrate 1001 and over the top surfaces ofthe transistors 1020 may be etched away, leaving behind the backboneliner 1021 only over vertical surfaces. Such an etching process may beused to form a device similar to those described with respect to FIGS.9A and 9B.

Referring now to FIG. 10D, a perspective view illustration of thesemiconductor device 1000 after a backbone 1010 is disposed over thebackbone liner 1021 is shown, in accordance with an embodiment. Thebackbone 1010 may be an insulative material that is etch selective tothe backbone liner 1021.

Referring now to FIG. 10E, a perspective view illustration of thesemiconductor device 1000 after portions of the backbone 1010 and thebackbone liner 1021 outside of the backbone trench 1095 are removed isshown, in accordance with an embodiment. The portions outside of thebackbone trench 1095 may be removed with an etching process with a masklayer (not shown) protecting the backbone trench 1095.

Referring now to FIG. 10F, a perspective view illustration of thesemiconductor device 1000 after a gate structure is disposed over thetransistors 1020 is shown, in accordance with an embodiment. The gatestructure may comprise a dummy gate electrode 1013′ with spacers 1011 oneither side. The gate structure may cross over a top surface of thebackbone 1010.

Referring now to FIG. 10G, a perspective view illustration of thesemiconductor device 1000 after source/drain recesses are made is shown,in accordance with an embodiment. In an embodiment, the recesses aremade by removing portions of the layers 1093, 1094 outside of thespacers 1011. Surfaces of the semiconductor channels 1006 that passthrough the spacers 1011 are visible in FIG. 10G.

Referring now to FIG. 10H, a perspective view illustration of thesemiconductor device 1000 after source/drain regions 1005 are formed isshown, in accordance with an embodiment. In an embodiment, thesource/drain regions 1005 may be grown with an epitaxial growth process.

Referring now to FIG. 10I, a perspective view illustration of a portionof the semiconductor device 1000 after the dummy gate electrode 1013′ isremoved is shown, in accordance with an embodiment. In an embodiment, aninsulative layer 1003 may be disposed over the source/drain regions1005. As shown, removal of the dummy gate electrode 1013′ exposes thesemiconductor channels 1006, the backbone liner 1021, and the backbone1010.

Referring now to FIG. 10J, a cross-sectional illustration of thesemiconductor device 1000 in FIG. 10I is shown, in accordance with anembodiment. As shown, the semiconductor channels 1006 are in directcontact with the backbone liner 1021. The backbone liner 1021 may coversidewall surfaces of the backbone 1010 and a bottom surface of thebackbone 1010. In other embodiments, the backbone liner 1021 is absentfrom the bottom surface of the backbone 1010.

Referring now to FIG. 10K, a cross-sectional illustration of thesemiconductor device 1000 after portions of the backbone liner 1021 areremoved is shown, in accordance with an embodiment. As shown, removingthe backbone liner 1021 provides a gap 1097 between a surface of thesemiconductor channel 1006 and the surface of the backbone 1010. The gap1097 provides sufficient space to form the gate dielectric and gateelectrode around an entire perimeter of the semiconductor channel 1006.

Referring now to FIG. 10L, a cross-sectional illustration of thesemiconductor device 1000 after a gate stack is disposed over thesemiconductor channels 1006 is shown, in accordance with an embodiment.In an embodiment, the gate stack comprises a gate dielectric 1008 thatsurrounds an entire perimeter of the semiconductor channels 1006.Portions of the gate dielectric 1008 may be disposed over the backbone1010 and on the substrate 1001 due to a conformal deposition process. Inan embodiment, a gate electrode 1013 is disposed over the gatedielectric 1008. As such, GAA control of the forksheet transistors ofthe semiconductor device 1000 is provided.

Referring now to FIG. 11A, a cross-sectional illustration of asemiconductor device 1100 is shown, in accordance with an additionalembodiment. The plane of the cross-section in FIG. 11A is through thechannel region. The semiconductor device 1100 may comprise a substrate1101 and a plurality of forksheet transistors 1120 _(A-C) above thesubstrate 1101. The transistors 1120 may each comprise a plurality ofsemiconductor channels 1106. The semiconductor channels 1106 haveperimeters that are completely surrounded by a gate dielectric 1108 anda gate electrode 1113.

Each of the transistors 1120 may be separated from the neighboringtransistor 1120 by a backbone 1110. As opposed to the embodiments abovein FIGS. 8A-9B, a liner 1121 may be present in the channel regionbetween the backbone 1110 and the semiconductor channels 1106. This ispossible because the liner 1121 may comprise a catalytic oxidantmaterial. For example, the liner 1121 may comprise alumina. When astructure with a catalytic oxidant is adjacent to a semiconductormaterial, such as the channel 1106, the application of heat results in aportion of the channel 1106 and a portion of the liner 1121 beingoxidized. Subsequently, an etchant (e.g., a wet etch or an atomic layeretch (ALE) approach) that is selective to the oxide over thesemiconductor channel can be applied in the channel region to remove theoxides and create a gap between the remaining portion of the channel1106 and the remaining portion of the liner 1121. The gap allowssufficient room to deposit the gate dielectric 1108 and the gateelectrode 1113 completely around the perimeter of the channel 1106.

Additionally, since the oxidation reaction is localized to the region ofthe liner 1121 adjacent to the channels 1106, a pattern of recesses 1124may be present in the surface of the liner 1121 that faces the gateelectrode 1113. In an embodiment, the recesses 1124 are aligned with thechannels 1106. However, in other embodiments, the liner 1121 may becompletely removed.

In FIG. 11A, the recesses 1124 are shown as having a substantiallyrectangular profile. It is to be appreciated that in some embodiments,the recesses 1124 may have a shape that is more characteristic of adiffusion event. FIG. 11B is a zoomed in illustration of a region 1123that more clearly illustrates what a typical recess may look like. Forexample, the recesses 1124 may be bowl shaped, or have an otherwisenon-vertical surface. FIG. 11B also illustrates the consumed portion ofthe channel 1106′ (indicated with dashed lines). As shown, the channel1106 is originally coplanar with the surface of the liner 1121 beforethe oxidization and etching process.

Referring now to FIG. 11C, an example of another embodiment of thezoomed in region 1123 is shown. In FIG. 11C, the gate electrode 1113 (orthe workfunction metal (not shown), does not completely cover allsurfaces of the gate dielectric 1108 around the channel 1106. That is, avoid 1125 may be present at some locations. A void 1125 may prevent GAAcontrol of the channel 1106. However, in some embodiments, a portion ofthe surface of the channel 1106 facing the backbone 1110 may still begated to provide at least some additional control of the channel 1106.

Referring now to FIGS. 12A-12D a series of illustrations depicting aprocess to form a GAA forksheet architecture using a liner with acatalytic oxidant is shown, in accordance with an embodiment.

Referring now to FIG. 12A, a cross-sectional illustration of asemiconductor device 1200 is shown, in accordance with an embodiment.The cross-sectional view depicts a cross-section of the channel region,with backbones 1210 separating individual transistors. In an embodiment,a liner 1221 is disposed along sidewalls of the backbones 1210. In someembodiments, the liner 1221 may also be over a bottom surface of thebackbones 1210 over the substrate 1201. In an embodiment, the liners1221 may comprise a catalytic oxidant material. For example, the liners1221 may comprise alumina. In an embodiment, the semiconductor channels1206 are in direct contact with the liners 1221.

Referring now to FIG. 12B, a cross-sectional illustration of thesemiconductor device 1200 after a heat treatment is shown, in accordancewith an embodiment. In an embodiment, the heat treatment results inlocal oxidation of the liner 1221. For example, only portions of theliner 1221 that are proximate to the semiconductor channels 1206 areoxidized. Oxidized portions 1221′ of the liner 1221 are shown with adifferent shading in FIG. 12B. In an embodiment, portions 1206′ of thesemiconductor channels may also be oxidized during the heat treatment.

Referring now to FIG. 12C, a cross-sectional illustration of thesemiconductor device 1200 after the oxidized portions 1206′ and 1221′are removed is shown, in accordance with an embodiment. In anembodiment, the oxidized portions 1206′ and 1221′ may be removed withone or more etching processes that are selective to the semiconductorchannels 1206 and/or the liner 1221. As such, recesses 1224 are formedinto the liner 1221.

Referring now to FIG. 12D, a cross-sectional illustration of thesemiconductor device 1200 after a gate stack is disposed over thesemiconductor channels 1206 is shown, in accordance with an embodiment.In an embodiment, the gate stack may comprise a gate dielectric 1208 anda gate electrode 1213. The recess 1224 provides sufficient space for thegate dielectric 1208 and the gate electrode 1213 to completely surroundthe perimeter of the semiconductor channels 1206. As such, GAA controlis provided in the semiconductor device 1200.

Referring now to FIGS. 13A-13C, a series of cross-sectionalillustrations depicting a process to form an interconnect between thegate electrodes of two forksheet transistors that passes across thebackbone is shown, in accordance with an embodiment.

Referring now to FIG. 13A, a cross-sectional illustration of asemiconductor device 1300 is shown, in accordance with an embodiment. Inan embodiment, the semiconductor device 1300 comprises a substrate 1301,and a first transistor 1320 _(A) and a second transistor 1320 _(B) overthe substrate 1301. The first transistor 1320 _(A) may be separated fromthe second transistor 1320 _(B) by a backbone 1310. In the illustratedembodiment, the semiconductor channels 1306 of the transistors 1320extend out from the backbone 1310. In other embodiments, thesemiconductor channels 1306 may have a GAA architecture similar to thearchitectures described above with respect to FIGS. 8A-9B or FIGS.11A-11C. The channels 1306 may be surrounded by a gate electrode 1313,and an insulator 1303 may surround the transistors 1320. In anembodiment, the first transistor 1320 _(A) may be a first conductivitytype (e.g., P-type) and the second transistor 1320 _(B) may be a secondconductivity type (e.g., N-type). In other embodiments, the firsttransistor 1320 _(A) and the second transistor 1320 _(B) may be the sameconductivity type.

Referring now to FIG. 13B, a cross-sectional illustration of thesemiconductor device 1300 after the backbone 1310 is etched back isshown, in accordance with an embodiment. In an embodiment, the backbone1310 may be etched with a timed etching process. The etching process istimed so that a top surface 1332 of the backbone 1310 is above (in theZ-direction) the top surfaces 1333 of the channels 1306. Keeping the topsurface 1332 of the backbone 1310 above the channels 1306 preventsshorting to the channels 1306 when the interconnect is disposed in therecess 1331.

Referring now to FIG. 13C, a cross-sectional illustration of thesemiconductor device 1300 after an interconnect 1334 is disposed in therecess 1331 is shown, in accordance with an embodiment. The interconnect1334 provides an electrical connection between the gate electrode 1313of the first transistor 1320 _(A) and the gate electrode 1313 of thesecond transistor 1320 _(B). In an embodiment, the interconnect 1334 isthe same material as one or both of the gate electrodes 1313. In otherembodiments, the interconnect 1334 is a different material than the gateelectrodes 1313.

Referring now to FIG. 13D, a plan view illustration of the semiconductordevice 1300 in FIG. 13C is shown, in accordance with an embodiment. Inan embodiment, the transistors 1320 include source/drains 1305 onopposite sides of the gate electrode 1313. The source/drains 1305 may beseparated from the gate electrode 1313 by a spacer 1311. As shown, theinterconnect 1334 is isolated to a portion of the backbone 1310 that isbetween the spacers 1311 in order to only provide an electricalconnection through backbone 1310 within the channel region.

Referring now to FIGS. 14A-14C, a series of cross-sectionalillustrations depicting a process for forming an interconnect betweenthe gate electrodes across a backbone using an etchstop layer is shown,in accordance with an embodiment.

Referring now to FIG. 14A, a cross-sectional illustration of asemiconductor device 1400 is shown, in accordance with an embodiment. Inan embodiment, the semiconductor device 1400 comprises a substrate 1401,and a first transistor 1420 _(A) and a second transistor 1420 _(B) overthe substrate 1401. The first transistor 1420 _(A) may be separated fromthe second transistor 1420 _(B) by a backbone 1410. In the illustratedembodiment, the semiconductor channels 1406 of the transistors 1420extend out from the backbone 1410. In other embodiments, thesemiconductor channels 1406 may have a GAA architecture similar to thearchitectures described above with respect to FIGS. 8A-9B or FIGS.11A-11C. The channels 1406 may be surrounded by a gate electrode 1413,and an insulator 1403 may surround the transistors 1420. In anembodiment, the first transistor 1420 _(A) may be a first conductivitytype (e.g., P-type) and the second transistor 1420 _(B) may be a secondconductivity type (e.g., N-type). In other embodiments, the firsttransistor 1420 _(A) and the second transistor 1420 _(B) may be the sameconductivity type.

In an embodiment, the backbone 1410 may further comprise an etchstoplayer 1435. The etchstop layer 1435 may have a high etch selectivitywith respect to the remaining portion of the backbone 1410. As such, theportion of the backbone 1410 above the etchstop layer 1435 may be etchedaway without the tight process control needed in a timed etchingprocess, such as the process described above with respect to FIGS.13A-13C. In an embodiment, a top surface 1436 of the etchstop layer 1435is above a top surface 1433 of the channels 1406. This prevents shortingto the channels after deposition of the interconnect between the gateelectrodes 1413.

Referring now to FIG. 14B, a cross-sectional illustration of thesemiconductor device 1400 after the top portion of the backbone 1410 isetched back is shown, in accordance with an embodiment. Removing the topportion of the backbone 1410 results in the formation of a recess 1431that ends at the top surface of the etchstop layer 1435.

Referring now to FIG. 14C, a cross-sectional illustration of thesemiconductor device 1400 after an interconnect is disposed in therecess 1431 is shown, in accordance with an embodiment. The interconnect1434 provides an electrical connection between the gate electrode 1413of the first transistor 1420 _(A) and the gate electrode 1413 of thesecond transistor 1420 _(B). In an embodiment, the interconnect 1434 isthe same material as one or both of the gate electrodes 1413. In otherembodiments, the interconnect 1434 is a different material than the gateelectrodes 1413.

Referring now to FIGS. 15A-15D, cross-sectional illustrations ofsemiconductor devices 1500 are shown, in accordance with variousembodiments. The illustrated embodiments depict different configurationsof an etchstop layer that may be used in conjunction with the backbonein order to provide interconnects across the backbone.

Referring now to FIG. 15A, a cross-sectional illustration of asemiconductor device 1500 is shown, in accordance with an embodiment. Inan embodiment, the semiconductor device 1500 comprises a substrate 1501,and a first transistor 1520 _(A) and a second transistor 1520 _(B) overthe substrate 1501. The first transistor 1520 _(A) may be separated fromthe second transistor 1520 _(B) by a backbone 1510. In the illustratedembodiment, the semiconductor channels 1506 of the transistors 1520extend out from the backbone 1510. In other embodiments, thesemiconductor channels 1506 may have a GAA architecture similar to thearchitectures described above with respect to FIGS. 8A-9B or FIGS.11A-11C. The channels 1506 may be surrounded by a gate electrode 1513,and an insulator 1503 may surround the transistors 1520. In anembodiment, the first transistor 1520 _(A) may be a first conductivitytype (e.g., P-type) and the second transistor 1520 _(B) may be a secondconductivity type (e.g., N-type). In other embodiments, the firsttransistor 1520 _(A) and the second transistor 1520 _(B) may be the sameconductivity type.

In an embodiment, the backbone 1510 comprises a pair of etchstop layers1535 _(A) and 1535 _(B). The first etchstop 1535 _(A) layer has a topsurface 1536 that is above a top surface 1533 of the topmost channels1506. The second etchstop layer 1535 _(B) has a bottom surface 1537 thatis below the bottom surface 1538 of the bottommost channels 1506.Accordingly, interconnects (not shown) between the gate electrodes 1513may be made across the backbone 1510 above and below the channels 1506.

Referring now to FIG. 15B, a cross-sectional illustration of asemiconductor device 1500 is shown, in accordance with an additionalembodiment. The semiconductor device 1500 in FIG. 15B may besubstantially similar to the semiconductor device 1500 in FIG. 15A,except that a single etchstop layer 1535 is used. The top surface 1536of the etchstop layer 1535 is above the top surface 1533 of the topmostchannels 1506, and a bottom surface 1537 of the etchstop layer 1535 isbelow the bottom surface 1538 of the bottommost channel 1506.

Referring now to FIG. 15C, a cross-sectional illustration of asemiconductor device 1500 is shown, in accordance with an additionalembodiment. The semiconductor device 1500 in FIG. 15C may besubstantially similar to the semiconductor device 1500 in FIG. 15B,except that the bottom surface 1537 of the etchstop layer 1535 extendsall the way to the substrate 1501.

Referring now to FIG. 15D, a cross-sectional illustration of asemiconductor device 1500 is shown, in accordance with an additionalembodiment. The semiconductor device 1500 in FIG. 15D may besubstantially similar to the semiconductor device 1500 in FIG. 15A,except that the etchstop layer 1535 is positioned at the bottom of thebackbone 1510. In an embodiment, a bottom surface 1537 of the etchstoplayer 1535 is below a bottom surface 1538 of a bottommost channel 1506.

Referring now to FIGS. 16A-16D, cross-sectional illustrations along thelength of the backbone 1610 are shown, in accordance with an embodiment.In an embodiment, the semiconductor channels 1606 are illustrated withdashed lines to indicate that they are into and out of the plane ofFIGS. 16A-16D. Additionally, the locations of the source/drains 1605 arehighlighted as being on opposite ends of the gate stack 1612.

Referring now to FIG. 16A, a cross-sectional illustration of thebackbone 1610 is shown, in accordance with an embodiment. As shown, theetchstop layer 1635 extends along an entire length of the backbone 1610.That is the etchstop layer 1635 is positioned adjacent to the gate stack1612 and the source/drain regions 1605. The etchstop layer 1635 is shownin a position (in the Z-direction) similar to the embodiment shown inFIGS. 14A-C. However, it is to be appreciated that the etchstop layer1635 (or a plurality of etchstop layers 1635) may be located in anyposition (e.g., in the positions illustrated in FIGS. 15A-D).

In FIG. 16B, a cross-sectional illustration of the backbone 1610 afteran interconnect 1634 is formed through the backbone 1610 is shown, inaccordance with an embodiment. As shown, the interconnect 1634 isdisposed in a recess in the backbone 1610. Additionally, theinterconnect 1634 is isolated to the gate stack 1612.

Referring now to FIGS. 16C and 16D, cross-sectional illustrations of abackbone 1610 before and after an interconnect 1634 is formed across thebackbone 1610 is shown, in accordance with an embodiment. The backbone1610 in FIGS. 16C and 16D are similar to those in FIGS. 16A and 16B,with the exception that the etchstop layer 1635 does not extend along anentire length of the backbone 1610. For example, the etchstop layer 1635may be located proximate to the gate stack 1612. In some embodiments,the etchstop layer 1635 may extend beyond the gate stack 1612 withoutextending along the entire length of the backbone 1610.

Referring now to FIG. 17A, a cross-sectional illustration of asemiconductor device 1700 is shown, in accordance with an embodiment. Inan embodiment, the semiconductor device 1700 comprises a substrate 1701and a pair of forksheet transistor 1720 _(A) and 1720 _(B) over thesubstrate 1701. The forksheet transistors 1720 may be separated fromeach other by a backbone 1710. The plane of the illustrated embodimentis through the source/drain region 1705. The location of the channels1706 are shown with dashed lines to indicate they are out of the planeshown in FIG. 17A. In an embodiment, the first transistor 1720 _(A) maybe a first conductivity type (e.g., P-type) and the second transistor1720 _(B) may be a second conductivity type (e.g., N-type). In otherembodiments, the first transistor 1720 _(A) and the second transistor1720 _(B) may be the same conductivity type. As shown, an interconnect1741 is disposed through the backbone 1710 in order to electricallycouple the source/drain region 1705 of the first transistor 1720 _(A) tothe source/drain region 1705 of the second transistor 1720 _(B).

Referring to FIG. 17B, a plan view illustration of the semiconductordevice 1700 in FIG. 17A is shown, in accordance with an embodiment. InFIG. 17B, the gate electrode 1713 and spacers 1711 are shown between thesource/drain regions 1705 of each transistor 1720. Additionally, it isshown that the interconnect 1741 is isolated to a single side of thetransistors 1720. For example, the bottom source/drain region 1705 (asviewed in FIG. 17B) of the first transistor 1720 _(A) is electricallycoupled to the bottom source/drain region 1705 (as viewed in FIG. 17B)of the second transistor 1720 _(B).

Referring now to FIG. 18, a plan view illustration of a semiconductordevice 1800 is shown, in accordance with an additional embodiment. Thesemiconductor device 1800 comprises a first forksheet transistor 1820_(A) and a second forksheet transistor 1820 _(B) that are separated by abackbone 1810. Each transistor 1820 comprises source/drain regions 1805that are on opposite ends of the gate electrode 1813 and spacers 1811.The semiconductor channels connecting the source/drain regions 1805 arehidden by the gate electrode 1813. In an embodiment, the firsttransistor 1820 _(A) may be a first conductivity type (e.g., P-type) andthe second transistor 1820 _(B) may be a second conductivity type (e.g.,N-type). In other embodiments, the first transistor 1820 _(A) and thesecond transistor 1820 _(B) may be the same conductivity type.

As shown, the semiconductor device 1800 comprises a first interconnect1834 and a second interconnect 1841. The first interconnect 1834electrically couples the gate electrodes 1813 of the first transistor1820 _(A) and the second transistor 1820 _(B). The first interconnect1834 may be similar to the interconnects described above with respect toFIGS. 13A-16D. The second interconnect 1841 electrically couples thesource/drain regions 1805 of the first transistor 1820 _(A) and thesecond transistor 1820 _(B). The second interconnect 1841 may be similarto the interconnects described above with respect to FIGS. 17A and 17B.In an embodiment, providing interconnects 1834 and 1841 may allow forsemiconductor device 1800 to be wired as an inverter. Other circuitelements may also be formed by providing various interconnects throughthe backbone 1810 to connect the source/drain regions 1805 and/or thegate electrodes 1813.

Referring now to FIG. 19A, a cross-sectional illustration of asemiconductor device 1900 is shown, in accordance with an embodiment. Inan embodiment, the semiconductor device 1900 comprises a substrate 1901and forksheet transistors 1920 _(A) and 1920 _(B) over the substrate1901. A backbone 1910 separates the first transistor 1920 _(A) from thesecond transistor 1920 _(B). The plane of the illustrated embodiment isthrough the source/drain region 1905. The location of the channels 1906are shown with dashed lines to indicate they are out of the plane shownin FIG. 19A. In an embodiment, the first transistor 1920 _(A) may be afirst conductivity type (e.g., P-type) and the second transistor 1920_(B) may be a second conductivity type (e.g., N-type). In otherembodiments, the first transistor 1920 _(A) and the second transistor1920 _(B) may be the same conductivity type.

In an embodiment, conductive features may be provided in the substrate1901. For example, a buried line 1918 may be positioned adjacent to thetransistors 1920. Conductive pads 1919 may be located below thetransistors 1920 and connected to the buried line 1918 (out of the planeof FIG. 19A). It is to be appreciated that the architecture of theconductive features in FIG. 19A is exemplary in nature, and that anybackside interconnect architecture may be used. For example, thebackside interconnect architecture may include any number of layers ofrouting, vias, pads, and the like.

In an embodiment, etch selective layers 1943 may be positioned betweenthe source/drain regions 1905 and the pads 1919. In a particularembodiment, the etch selective layers 1943 may be aligned with theoverlying channels 1906. For example, a distance between the backbone1910 and a surface 1942 of the channels 1906 facing away from thebackbone 1910 may be equal to a distance between the backbone 1910 and asurface 1944 of the etch selective layers 1943 facing away from thebackbone 1910. In some instances, the etch selective layers 1943 may bereferred to as being self-aligned with the overlying channels 1906. Theself-alignment may result from the patterning of the channels 1906 andthe etch selective layers 1943 with the same lithograph process (e.g., asingle mask). In an embodiment, the etch selective layers 1943 may be amaterial that is etch selective to the surrounding materials. In aparticular embodiment, the etch selective layers comprise titaniumnitride, though other materials may also be used.

Referring now to FIG. 19B, a cross-sectional illustration of thesemiconductor device 1900 after an interconnect 1941 is disposed acrossthe backbone 1910 is shown, in accordance with an embodiment. In theillustrated embodiment, the etch selective layers 1943 are not etchedaway. That is, the etch selective layers 1943 serve as an etch stop thatprevents the interconnect 1941 from contacting the underlying pads 1919.

Referring now to FIG. 19C, a cross-sectional illustration of thesemiconductor device 1900 with an interconnect 1941 that passes throughthe etch selective layers 1943 is shown, in accordance with anembodiment. In some embodiments, remnant portions 1943′ of the etchselective layers 1943 may remain adjacent to the interconnect 1941. Theinterconnect 1941 may contact the underlying pads 1919. As those skilledin the art will appreciated, in a single semiconductor die, there may beinstances where the etch selective layers 1943 remain to preventconnection to the underlying pads 1919 (e.g., similar to FIG. 19B), inaddition to instances where only remnant portions 1943′ of the etchselective layers 1943 remain. In yet another embodiment, the entirety ofthe etch selective layers 1943 below individual ones of the transistors1920 may be removed.

Referring now to FIG. 20_(A) , a cross-sectional illustration of asemiconductor device 2000 is shown, in accordance with an embodiment.The semiconductor device 2000 may be substantially similar to thesemiconductor device 1900, with the exception that a first etchselective layer 2043 _(A) comprises a different material than a secondetch selective layer 2043 _(B). For example, the first etch selectivelayer 2043 _(A) may have an etch selectivity with respect to the secondetch selective layer 2043 _(B). As such, one of the first etch selectivelayer 2043 _(A) or the second etch selective layer 2043 _(B) may beremoved without removing the other etch selective layer 2043 _(A) or2043 _(B).

In an embodiment, the semiconductor device 2000 comprises a substrate2001 and forksheet transistors 2020 _(A) and 2020 _(B) over thesubstrate 2001. A backbone 2010 separates the first transistor 2020 _(A)from the second transistor 2020 _(B). The plane of the illustratedembodiment is through the source/drain regions 2005. The location of thechannels 2006 are shown with dashed lines to indicate they are out ofthe plane shown in FIG. 20_(A) . In an embodiment, the first transistor2020 _(A) may be a first conductivity type (e.g., P-type) and the secondtransistor 2020 _(B) may be a second conductivity type (e.g., N-type).In other embodiments, the first transistor 2020 _(A) and the secondtransistor 2020 _(B) may be the same conductivity type.

In an embodiment, conductive features may be provided in the substrate2001. For example, a buried line 2018 may be positioned adjacent to thetransistors 2020. Conductive pads 2019 may be located below thetransistors 2020 and connected to the buried line 2018 (out of the planeof FIG. 20A). It is to be appreciated that the architecture of theconductive features in FIG. 20A is exemplary in nature, and that anybackside interconnect architecture may be used. For example, thebackside interconnect architecture may include any number of layers ofrouting, vias, pads, and the like.

Referring now to FIG. 20B, a cross-sectional illustration of thesemiconductor device 2000 after an interconnect 2041 across the backbone2010 is provided is shown, in accordance with an embodiment. As shown,only the first etch selective layer 2043 _(A) is etched to leave a firstremnant portion 2043 _(A)′. The second etch selective layer 2043 _(B)remains substantially unaltered. As such, the interconnect 2041 onlycontacts the pad 2019 below the first transistor 2020 _(A), and the pad2019 below the second transistor 2020 _(B) is electrically isolated fromthe interconnect 2041. As such, further refinement and control ofinterconnect layouts is provided when multiple etch selective layers2043 with different etch selectivities are used.

FIG. 21 illustrates a computing device 2100 in accordance with oneimplementation of an embodiment of the disclosure. The computing device2100 houses a board 2102. The board 2102 may include a number ofcomponents, including but not limited to a processor 2104 and at leastone communication chip 2106. The processor 2104 is physically andelectrically coupled to the board 2102. In some implementations the atleast one communication chip 2106 is also physically and electricallycoupled to the board 2102. In further implementations, the communicationchip 2106 is part of the processor 2104.

Depending on its applications, computing device 2100 may include othercomponents that may or may not be physically and electrically coupled tothe board 2102. These other components include, but are not limited to,volatile memory (e.g., DRAM), non-volatile memory (e.g., ROM), flashmemory, a graphics processor, a digital signal processor, a cryptoprocessor, a chipset, an antenna, a display, a touchscreen display, atouchscreen controller, a battery, an audio codec, a video codec, apower amplifier, a global positioning system (GPS) device, a compass, anaccelerometer, a gyroscope, a speaker, a camera, and a mass storagedevice (such as hard disk drive, compact disk (CD), digital versatiledisk (DVD), and so forth).

The communication chip 2106 enables wireless communications for thetransfer of data to and from the computing device 2100. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. The communication chip 2106 may implementany of a number of wireless standards or protocols, including but notlimited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE,GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well asany other wireless protocols that are designated as 3G, 4G, 5G, andbeyond. The computing device 2100 may include a plurality ofcommunication chips 2106. For instance, a first communication chip 2106may be dedicated to shorter range wireless communications such as Wi-Fiand Bluetooth and a second communication chip 2106 may be dedicated tolonger range wireless communications such as GPS, EDGE, GPRS, CDMA,WiMAX, LTE, Ev-DO, and others.

The processor 2104 of the computing device 2100 includes an integratedcircuit die packaged within the processor 2104. In an embodiment, theintegrated circuit die of the processor 2104 may comprise forksheettransistors, such as those described herein. The term “processor” mayrefer to any device or portion of a device that processes electronicdata from registers and/or memory to transform that electronic data intoother electronic data that may be stored in registers and/or memory.

The communication chip 2106 also includes an integrated circuit diepackaged within the communication chip 2106. In an embodiment, theintegrated circuit die of the communication chip 2106 may compriseforksheet transistors, such as those described herein.

In further implementations, another component housed within thecomputing device 2100 may comprise forksheet transistors, such as thosedescribed herein.

In various implementations, the computing device 2100 may be a laptop, anetbook, a notebook, an ultrabook, a smartphone, a tablet, a personaldigital assistant (PDA), an ultra mobile PC, a mobile phone, a desktopcomputer, a server, a printer, a scanner, a monitor, a set-top box, anentertainment control unit, a digital camera, a portable music player,or a digital video recorder. In further implementations, the computingdevice 2100 may be any other electronic device that processes data.

FIG. 22 illustrates an interposer 2200 that includes one or moreembodiments of the disclosure. The interposer 2200 is an interveningsubstrate used to bridge a first substrate 2202 to a second substrate2204. The first substrate 2202 may be, for instance, an integratedcircuit die. The second substrate 2204 may be, for instance, a memorymodule, a computer motherboard, or another integrated circuit die. In anembodiment, one of both of the first substrate 2202 and the secondsubstrate 2204 may comprise forksheet transistors, in accordance withembodiments described herein. Generally, the purpose of an interposer2200 is to spread a connection to a wider pitch or to reroute aconnection to a different connection. For example, an interposer 2200may couple an integrated circuit die to a ball grid array (BGA) 2206that can subsequently be coupled to the second substrate 2204. In someembodiments, the first and second substrates 2202/2204 are attached toopposing sides of the interposer 2200. In other embodiments, the firstand second substrates 2202/204 are attached to the same side of theinterposer 2200. And in further embodiments, three or more substratesare interconnected by way of the interposer 2200.

The interposer 2200 may be formed of an epoxy resin, afiberglass-reinforced epoxy resin, a ceramic material, or a polymermaterial such as polyimide. In further implementations, the interposer2200 may be formed of alternate rigid or flexible materials that mayinclude the same materials described above for use in a semiconductorsubstrate, such as silicon, germanium, and other group III-V and groupIV materials

The interposer 2200 may include metal interconnects 2208 and vias 2210,including but not limited to through-silicon vias (TSVs) 2212. Theinterposer 2200 may further include embedded devices 2214, includingboth passive and active devices. Such devices include, but are notlimited to, capacitors, decoupling capacitors, resistors, inductors,fuses, diodes, transformers, sensors, and electrostatic discharge (ESD)devices. More complex devices such as radio-frequency (RF) devices,power amplifiers, power management devices, antennas, arrays, sensors,and MEMS devices may also be formed on the interposer 2200. Inaccordance with embodiments of the disclosure, apparatuses or processesdisclosed herein may be used in the fabrication of interposer 2200.

Thus, embodiments of the present disclosure may comprise forksheettransistors, and the resulting structures.

The above description of illustrated implementations of the invention,including what is described in the Abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific implementations of, and examples for, the invention aredescribed herein for illustrative purposes, various equivalentmodifications are possible within the scope of the invention, as thoseskilled in the relevant art will recognize.

These modifications may be made to the invention in light of the abovedetailed description. The terms used in the following claims should notbe construed to limit the invention to the specific implementationsdisclosed in the specification and the claims. Rather, the scope of theinvention is to be determined entirely by the following claims, whichare to be construed in accordance with established doctrines of claiminterpretation.

Example 1: a semiconductor device, comprising: a first transistorstrata, wherein the first transistor strata comprises: a first backbone;a first transistor adjacent to a first edge of the first backbone; and asecond transistor adjacent to a second edge of the first backbone; and asecond transistor strata over the first transistor strata, wherein thesecond transistor strata comprises: a second backbone; a thirdtransistor adjacent to a first edge of the second backbone; and a fourthtransistor adjacent to a second edge of the second backbone.

Example 2: the semiconductor device of Example 1, wherein individualones of the first transistor, the second transistor, the thirdtransistor, and the fourth transistor comprise: a source; a drain; asemiconductor channel between the source and the drain; a gatedielectric surrounding portions of the semiconductor channel; and a gateelectrode over the gate dielectric.

Example 3: the semiconductor device of Example 2, wherein a surface ofthe semiconductor channel directly contacts the first backbone or thesecond backbone.

Example 4: the semiconductor device of Example 2, wherein thesemiconductor channel comprises a plurality of semiconductor channels ina vertical stack between the source and the drain.

Example 5: the semiconductor device of Examples 1-4, wherein the firstedge of the first backbone is offset from the first edge of the secondbackbone.

Example 6: the semiconductor device of Examples 1-5, wherein the firstedge of the first backbone is aligned with the first edge of the secondbackbone.

Example 7: the semiconductor device of Example 6, wherein the firstbackbone is connected to the second backbone.

Example 8: the semiconductor device of Examples 1-7, wherein the firsttransistor and the second transistor are P-type transistors, and whereinthe third transistor and the fourth transistor are N-type transistors.

Example 9: the semiconductor device of Examples 1-8, wherein the firsttransistor and the third transistor are P-type transistors, and whereinthe second transistor and the fourth transistor are N-type transistors.

Example 10: the semiconductor device of Examples 1-9, furthercomprising: an insulating layer between the first transistor strata andthe second transistor strata.

Example 11: the semiconductor device of Example 10, further comprising:an interconnect through the insulating layer to electrically couple agate electrode of the first transistor to a gate electrode of the thirdtransistor.

Example 12: the semiconductor device of Example 10, further comprising:an interconnect through the insulating layer to electrically couple asource or a drain of the first transistor to a source or a drain of thethird transistor.

Example 13: the semiconductor device of Example 12, wherein theinterconnect extends through the source or the drain of the thirdtransistor.

Example 14: the semiconductor device of Example 13, wherein theinterconnect passes into the source or the drain of the firsttransistor.

Example 15: the semiconductor device of Example 12, wherein theinterconnect contacts a perimeter of the source or the drain of thethird transistor, and wherein the interconnect contacts a perimeter ofthe source or drain of the first transistor.

Example 16: the semiconductor device of Examples 1-15, furthercomprising: a contact below the first transistor strata, wherein thecontact is separated from the first transistor strata by an insulatinglayer; and an interconnect through the insulating layer, wherein theinterconnect electrically couples the contact to the first transistor.

Example 17: the semiconductor device of Example 16, wherein theinterconnect electrically couples the contact to a source or a drain ofthe first transistor.

Example 18: the semiconductor device of Example 16, wherein theinterconnect electrically couples the contact to a gate electrode of thefirst transistor.

Example 19: a semiconductor device, comprising: a backbone having afirst edge and a second edge, wherein the backbone is an insulativematerial; a first transistor adjacent to the first edge of the backbone;and a second transistor adjacent to the second edge of the backbone,wherein individual ones of the first transistor and the secondtransistor comprise: a source; a drain; a semiconductor channel betweenthe source and the drain, wherein an edge of the semiconductor channelclosest to the backbone is spaced away from the first edge of thebackbone or the second edge of the backbone; a gate dielectriccompletely surrounding a perimeter of the semiconductor channel; and agate electrode completely surrounding the gate dielectric.

Example 20: the semiconductor device of Example 19, wherein the edge ofthe semiconductor channel closest to the backbone is spaced away fromthe first edge of backbone or the second edge of the backbone byapproximately 6 nm or less.

Example 21: the semiconductor device of Example 19 or Example 20,further comprising: a liner below the backbone, wherein the liner is amaterial that has an etch selectivity to a material of the backbone.

Example 22: the semiconductor device of Examples 19-21, furthercomprising: a liner over a portion of the first edge of the backbone andover a portion of the second edge of the backbone.

Example 23: the semiconductor device of Example 22, wherein the liner isbetween the source of the first transistor and the backbone, between thesource of the second transistor and the backbone, between the drain ofthe first transistor and the backbone, and between the drain of thesecond transistor and the backbone.

Example 24: the semiconductor device of Example 23, wherein a portion ofthe first edge of the backbone and a portion of the second edge of thebackbone adjacent to the gate electrode are not covered by the liner.

Example 25: the semiconductor device of Example 24, wherein a spacingbetween the backbone and an edge of the semiconductor channel closest tothe backbone is substantially equal to a thickness of the liner.

Example 26: the semiconductor device of Example 24, wherein the portionof the first edge of the backbone and the portion of the second edge ofthe backbone adjacent to the gate electrode are separated from the gateelectrodes by the gate dielectric.

Example 27: the semiconductor device of Examples 19-25, furthercomprising: a liner over the first edge of the backbone and over thesecond edge of the backbone, wherein the liner comprises a catalyticoxidant.

Example 28: the semiconductor device of Example 27, wherein thecatalytic oxidant comprises aluminum and oxygen.

Example 29: the semiconductor device of Example 27 or Example 28,wherein a surface of the liner facing the semiconductor channelcomprises a depression.

Example 30: the semiconductor device of Example 29, wherein thedepression is aligned with the semiconductor channel.

Example 31: the semiconductor device of Examples 19-30, furthercomprising: an air gap between the semiconductor channel and thebackbone.

Example 32: the semiconductor device of Examples 19-31, wherein thefirst transistor is an N-type transistor and the second transistor is aP-type transistor.

Example 33: the semiconductor device of Examples 19-32, wherein thesemiconductor channel comprises a plurality of semiconductor channels ina vertical stack between the source and the drain.

Example 34: a semiconductor device, comprising: a backbone having afirst edge and a second edge, wherein the backbone is an insulativematerial; a first transistor adjacent to the first edge of the backbone;a second transistor adjacent to the second edge of the backbone, whereinindividual ones of the first transistor and the second transistorcomprise: a source; a drain; a semiconductor channel between the sourceand the drain; a gate dielectric surrounding at least a portion of aperimeter of the semiconductor channel; and a gate electrode over thegate dielectric; and an interconnect to electrically couple the firsttransistor to the second transistor, wherein the interconnect passesthrough the backbone.

Example 35: the semiconductor device of Example 34, wherein theinterconnect connects the gate electrode of the first transistor to thegate electrode of the second transistor.

Example 36: the semiconductor device of Example 35, wherein the backbonecomprises a first layer and a second layer, wherein the first layer hasan etch selectivity to the second layer.

Example 37: the semiconductor device of Example 36, wherein a topsurface of the first layer is above a topmost surface of thesemiconductor channel of the first transistor and a topmost surface ofthe semiconductor channel of the second transistor, and wherein thesecond layer is adjacent to the semiconductor channel of the firsttransistor and the semiconductor channel of the second transistor.

Example 38: the semiconductor device of Example 37, wherein theinterconnect contacts the top surface over the second layer.

Example 39: the semiconductor device of Examples 36-38, wherein a bottomsurface of the first layer is below a bottommost surface of thesemiconductor channel of the first transistor and a bottommost surfaceof the semiconductor channel of the second transistor, and wherein thesecond layer is adjacent to the semiconductor channel of the firsttransistor and the semiconductor channel of the second transistor.

Example 40: the semiconductor device of Example 39, wherein theinterconnect contacts the bottom surface of the first layer.

Example 41: the semiconductor device of Examples 36-40, wherein a topsurface of the first layer is above a topmost surface of thesemiconductor channel of the first transistor and a topmost surface ofthe semiconductor channel of the second transistor, and wherein thesecond layer is above the first layer.

Example 42: the semiconductor device of Examples 36-41, wherein thesecond layer and the first layer both extend along an entire length ofthe backbone.

Example 43: the semiconductor device of Examples 36-41, wherein a lengthof the first layer is smaller than a length of the second layer.

Example 44: the semiconductor device of Example 43, wherein the firstlayer is aligned with the gate electrode of the first transistor and thegate electrode of the second transistor.

Example 45: the semiconductor device of Examples 34-44, wherein theinterconnect connects the source or the drain of the first transistor tothe source or the drain of the second transistor.

Example 46: the semiconductor device of Example 45, further comprising:a first etch selective layer below the first transistor; and a secondetch selective layer below the second transistor.

Example 47: the semiconductor device of Example 46, wherein the firstetch selective layer is the same material as the second etch selectivelayer.

Example 48: the semiconductor device of Example 46, wherein the firstetch selective layer has an etch selectivity with respect to the secondetch selective layer.

Example 49: the semiconductor device of Example 46, wherein a first edgeof the first etch selective layer that faces away from the backbone isspaced away from the backbone by a first spacing equal to a secondspacing between a second edge of the semiconductor channel of the firsttransistor that faces away from the backbone and the backbone, andwherein a third edge of the second etch selective layer that faces awayfrom the backbone is spaced away from the backbone by a third spacingequal to a fourth spacing between a fourth edge of the semiconductorchannel of the second transistor that faces away from the backbone andthe backbone.

Example 50: the semiconductor device of Example 49, wherein a width ofone or both of the first etch selective layer and the second etchselective layer is smaller than a width of the overlying semiconductorchannel.

Example 51: the semiconductor device of Example 46, wherein a bottominterconnect passes adjacent to one or both of the first etch selectivelayer and the second etch selective layer to electrically couple one orboth of the source or the drain of the first transistor to contactsbelow the first transistor and the second transistor.

Example 52: the semiconductor device of Examples 34-51, wherein theinterconnect comprises: a first interconnect that passes through thebackbone, wherein the first interconnect electrically couples the gateelectrode of the first transistor to the gate electrode of the secondtransistor; and a second interconnect that passes through the backbone,wherein the second interconnect electrically couples the source or thedrain of the first transistor to the source or the drain of the secondtransistor.

Example 53: the semiconductor device of Examples 34-52, wherein thesemiconductor device is an inverter.

Example 54: the semiconductor device of Examples 34-53, wherein thefirst transistor is an N-type transistor, and wherein the secondtransistor is a P-type transistor.

Example 55: the semiconductor device of Examples 34-53, wherein thesemiconductor channel comprises a plurality of semiconductor channels ina vertical stack between the source and the drain.

Example 56: an electronic system, comprising: a board; an electronicpackage connected to the board; and a die electrically coupled to theelectronic package, wherein the die comprises: a backbone having a firstedge and a second edge, wherein the backbone is an insulative material;a first transistor adjacent to the first edge of the backbone; a secondtransistor adjacent to the second edge of the backbone; and aninterconnect to electrically couple the first transistor to the secondtransistor, wherein the interconnect passes through the backbone.

Example 57: the electronic system of claim 56, wherein individual onesof the first transistor and the second transistor comprise: a source; adrain; a semiconductor channel between the source and the drain; a gatedielectric surrounding at least a portion of a perimeter of thesemiconductor channel; and a gate electrode over the gate dielectric.

Example 58: the electronic system of Example 57, wherein the gatedielectric completely surrounds a perimeter of the semiconductorchannel.

Example 59: the electronic system of Examples 56-58, further comprising:a third transistor over the first transistor; a fourth transistor overthe second transistor; and a second backbone between the thirdtransistor and the fourth transistor.

Example 60: the electronic system of Example 59, wherein the thirdtransistor is electrically coupled to the first transistor, wherein thefourth transistor is electrically coupled to the second transistor, orwherein the third transistor is electrically coupled to the firsttransistor and the fourth transistor is electrically coupled to thesecond transistor.

What is claimed is:
 1. A semiconductor device, comprising: a firsttransistor strata, wherein the first transistor strata comprises: afirst backbone; a first transistor adjacent to a first edge of the firstbackbone; and a second transistor adjacent to a second edge of the firstbackbone; and a second transistor strata over the first transistorstrata, wherein the second transistor strata comprises: a secondbackbone, the second backbone separate and distinct from the firstbackbone, and the second backbone at least partially verticallyoverlapping with the first backbone; a third transistor adjacent to afirst edge of the second backbone; and a fourth transistor adjacent to asecond edge of the second backbone.
 2. The semiconductor device of claim1, wherein individual ones of the first transistor, the secondtransistor, the third transistor, and the fourth transistor comprise: asource; a drain; a semiconductor channel between the source and thedrain; a gate dielectric surrounding portions of the semiconductorchannel; and a gate electrode over the gate dielectric.
 3. Thesemiconductor device of claim 2, wherein a surface of the semiconductorchannel directly contacts the first backbone or the second backbone. 4.The semiconductor device of claim 2, wherein the semiconductor channelcomprises a plurality of semiconductor channels in a vertical stackbetween the source and the drain.
 5. The semiconductor device of claim1, wherein the first edge of the first backbone is offset from the firstedge of the second backbone.
 6. The semiconductor device of claim 1,wherein the first edge of the first backbone is aligned with the firstedge of the second backbone.
 7. The semiconductor device of claim 6,wherein the first backbone is connected to the second backbone.
 8. Thesemiconductor device of claim 1, wherein the first transistor and thesecond transistor are P-type transistors, and wherein the thirdtransistor and the fourth transistor are N-type transistors.
 9. Thesemiconductor device of claim 1, wherein the first transistor and thethird transistor are P-type transistors, and wherein the secondtransistor and the fourth transistor are N-type transistors.
 10. Thesemiconductor device of claim 1, further comprising: an insulating layerbetween the first transistor strata and the second transistor strata.11. The semiconductor device of claim 10, further comprising: aninterconnect through the insulating layer to electrically couple a gateelectrode of the first transistor to a gate electrode of the thirdtransistor.
 12. The semiconductor device of claim 10, furthercomprising: an interconnect through the insulating layer to electricallycouple a source or a drain of the first transistor to a source or adrain of the third transistor.
 13. The semiconductor device of claim 12,wherein the interconnect extends through the source or the drain of thethird transistor.
 14. The semiconductor device of claim 13, wherein theinterconnect passes into the source or the drain of the firsttransistor.
 15. The semiconductor device of claim 12, wherein theinterconnect contacts a perimeter of the source or the drain of thethird transistor, and wherein the interconnect contacts a perimeter ofthe source or drain of the first transistor.
 16. The semiconductordevice of claim 1, further comprising: a contact below the firsttransistor strata, wherein the contact is separated from the firsttransistor strata by an insulating layer; and an interconnect throughthe insulating layer, wherein the interconnect electrically couples thecontact to the first transistor.
 17. The semiconductor device of claim16, wherein the interconnect electrically couples the contact to asource or a drain of the first transistor.
 18. The semiconductor deviceof claim 16, wherein the interconnect electrically couples the contactto a gate electrode of the first transistor.
 19. A semiconductor device,comprising: a backbone having a first edge and a second edge, whereinthe backbone is an insulative material, and a liner is over a portion ofthe first edge of the backbone and over a portion of the second edge ofthe backbone; a first transistor adjacent to the first edge of thebackbone; and a second transistor adjacent to the second edge of thebackbone, wherein individual ones of the first transistor and the secondtransistor comprise: a source; a drain; a semiconductor channel betweenthe source and the drain, wherein an edge of the semiconductor channelclosest to the backbone is spaced away from the first edge of thebackbone or the second edge of the backbone; a gate dielectriccompletely surrounding a perimeter of the semiconductor channel; and agate electrode completely surrounding the gate dielectric.
 20. Thesemiconductor device of claim 19, wherein the edge of the semiconductorchannel closest to the backbone is spaced away from the first edge ofbackbone or the second edge of the backbone by approximately 6 nm orless.
 21. An electronic system, comprising: a board; an electronicpackage connected to the board; and a die electrically coupled to theelectronic package, wherein the die comprises: a backbone having a firstedge and a second edge, wherein the backbone is an insulative material,and a liner is over a portion of the first edge of the backbone and overa portion of the second edge of the backbone; a first transistoradjacent to the first edge of the backbone; a second transistor adjacentto the second edge of the backbone; and an interconnect to electricallycouple the first transistor to the second transistor, wherein theinterconnect passes through the backbone.
 22. The electronic system ofclaim 21, wherein individual ones of the first transistor and the secondtransistor comprise: a source; a drain; a semiconductor channel betweenthe source and the drain; a gate dielectric surrounding at least aportion of a perimeter of the semiconductor channel; and a gateelectrode over the gate dielectric.
 23. The electronic system of claim22, wherein the gate dielectric completely surrounds a perimeter of thesemiconductor channel.
 24. A semiconductor device, comprising: abackbone having a first edge and a second edge, wherein the backbone isan insulative material; a liner below the backbone, wherein the liner isa material that has an etch selectivity to a material of the backbone; afirst transistor adjacent to the first edge of the backbone; and asecond transistor adjacent to the second edge of the backbone, whereinindividual ones of the first transistor and the second transistorcomprise: a source; a drain; a semiconductor channel between the sourceand the drain, wherein an edge of the semiconductor channel closest tothe backbone is spaced away from the first edge of the backbone or thesecond edge of the backbone; a gate dielectric completely surrounding aperimeter of the semiconductor channel; and a gate electrode completelysurrounding the gate dielectric.